6.12.65 64bit Fax Detection no dial tone

Recently I have installed FreePBX Distro 6.12.65 64bit
I’m using Asterisk 13 with an AEX410 PCI Express card which has 2 FXO & 2 FXS modules.
Everything works as it should except fax detection.
I enabled fax in an PJSIP extension (901) and set Fax Email & Attachment Format.
Then I went to my inbound route and set:
Detect Faxes: Yes
Fax Detection type: Dahdi
Fax Detection Time: 4
Fax Destination: Fax Receipient -> 901 extension I mentioned above.

Now, if I understand this correctly, since I set “Fax Detection Time: 4”, when someone calls, the call will be picked up by the inbound route, the caller will hear 4 rings, and if it’s a fax it will be passed to the associated extension (901), otherwise it’s considered a normal voice call so it will be passed to a queue (1001) I have set in the inbound route.
Did I understood this correctly, or am I missing something?

Now my problem is, that when someone calls, the inbound route picks up the call, the caller hears nothing (absolutute silence, no dial tone at all) for an equivalent time of 4 rings, and then the call is passed to the queue (1001) I have set.

Durring the fax detection phase (Fax Detection Time: 4) shouldn’t the caller hear dial tone?

I also tried setting Fax Detection Time: 10 and enabling Signal Ringing in the inbound route, but it didn’t help.
Any ideas?

Fax has been problematic for several people using Asterisk 13, I strongly recommend using v11 if at all possible.